Altair networking (#2300)

## Issue Addressed

Resolves #2278 

## Proposed Changes

Implements the networking components for the Altair hard fork https://github.com/ethereum/eth2.0-specs/blob/dev/specs/altair/p2p-interface.md

## Additional Info

This PR acts as the base branch for networking changes and tracks https://github.com/sigp/lighthouse/pull/2279 . Changes to gossip, rpc and discovery can be separate PRs to be merged here for ease of review.

Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/eth2_libp2p/Cargo.toml

@@ -40,12 +40,15 @@ rand = "0.7.3"
 directory = { path = "../../common/directory" }
 regex = "1.3.9"
 strum = { version = "0.20", features = ["derive"] }
+superstruct = "0.2.0"
 
 [dependencies.libp2p]
 #version = "0.39.1"
 #default-features = false
+# TODO: Update once https://github.com/libp2p/rust-libp2p/pull/2103 and 
+# https://github.com/libp2p/rust-libp2p/pull/2137 are merged upstream.
 git = "https://github.com/sigp/rust-libp2p"
-rev = "323cae1d08112052740834aa1fb262ae43e6f783"
+rev = "75fd53ec5407a58ae1ff600fd1c68ea49079364a"
 features = ["websocket", "identify", "mplex", "yamux", "noise", "gossipsub", "dns-tokio", "tcp-tokio"]
 
 [dev-dependencies]